Replace 3D image with building crypto

Update Hero to use uploaded building illustration replacing previous 3D model image; copy asset to src/assets/building-crypto.png and import via updated Hero.tsx. Remove previous 3D model references and display the new image in the hero section with hover-friendly styling. X-Lovable-Edit-ID: edt-bb83bfa9-3c3b-4958-96c2-800d70c79887